Real-time monitoring of a non-ambulatory patient's vital signs is typically achieved through non-invasive methods. For example, a patient in an operating room or ICU bed may have a blood pressure monitor with a cuff disposable about the upper arm; a pulse oximeter engaged around a fingertip; adhesive electrodes affixed to the skin (proximate to the heart) that measure the electrocardiogram and respiratory rate/pattern of respiration; an oral/aural thermometer that measures body temperature, and a stethoscope for monitoring heart/lung/airway sounds. These non-invasive vital signs sensors are often cumbersome and unwieldy. Patients that are hospitalized, immobilized, or stationary commonly tolerate the inconveniences inherent in non-invasive sensors. Continuous monitoring of hospitalized patients in the emergency room, operating room, intensive care unit, and catheterization laboratory may help medical professionals detect clinically significant changes in patient physiology. Vital sign trend data may be used to monitor and adjust medical and surgical therapy which may lead to decreased morbidity and mortality. Ambulatory patients may use telemedicine software programs to intermittently communicate with medical professionals at a remote location, using a computer program like Skype. A brief period of vital sign trend data may be transmitted via the internet to a central monitoring station for clinician interpretation. Intermittent home telemedicine has been successfully used to manage patients with conditions such as congestive heart failure, type 2 diabetes, influenza and premature labor outside of the emergency room and hospital.
A medical professional may order short-term recording of an ambulatory patient's vital sign data using non-invasive sensors for several days, weeks or months. The recorded trend data may be downloaded to a computer and interpreted to determine the clinical significance. The real-time monitoring of an ambulatory patient's vital signs, however, is more challenging owing to the patient's mobility, and lack of supervision by hospital staff. Many patients are not compliant obtaining frequent or timely vital sign measurement using non-invasive sensors. Moreover, even when a patient is attentive to compliance, the cumbersome nature of such devices often results in patient's either removing the devices or shifting the devices to a more comfortable position, which can create artifacts, inaccurate readings, and occlude blood flow. Moreover, non-invasive devices are typically less accurate and less stable than implantable sensors.
Short-term and long-term implantable intravascular blood pressure sensors have been devised to measure blood pressure in real-time. Catheters are sometimes inserted short-term into the peripheral artery of a patient to monitor arterial blood pressure and arterial pressure waveform. Long-term intravascular blood pressure sensors may be inserted into the bloodstream of large arteries and veins to chronically monitor research animals. However, such intravascular blood pressure sensors are prone to obstruct blood flow and cause endothelial cell injury, thrombosis, and emboli. Other long-term implantable blood pressure sensors are disposed around the outer diameter of an artery wall and use application to produce a robust mechanical coupling with the transducer's diaphragm.